This project is designed to further study the mechanisms of production and the biological significance of the detection of a lymphokine, secreted by lymphocytes of Cryptococcus neoformans infected mice, which is capable of inhibiting the phagocytic activity of a subpopulation of peritoneal macrophages. Previous studies have shown that this lymphokine can be produced by lymphocytes which are taken from animals injected with the soluble capsular polysaccharide of cryptococci. The present investigation will determine if other protein and polysaccharide antigens can elicit this response. In addition, the characteristics of the macrophage which is affected by the lymphokine will be examined in regard to its membrane markers, bouyant density, anatomic location and state of activation. The T-cell subset which is responsible for the generation of the factor will be examined. Further physical and chemical characterization of the factor will be performed. Inhibitory activity for phagocytosis of two species of fungi has previously been described. The current investigation will determine if phagocytosis due to interaction with Fc and complement receptors as well as inert particles is likewise affected. This study will determine if the intracellular killing mechanisms of phagocytic cells are affected by the macrophage inhibiting lymphokine. The biologic significance of factor production to cryptococcal disease will be examined.